Microplastics in the Rhine River – from the Swiss catchment towards the North Sea

Mani, Thomas. Microplastics in the Rhine River – from the Swiss catchment towards the North Sea. 2019, Doctoral Thesis, University of Basel, Faculty of Science.


Official URL: http://edoc.unibas.ch/diss/DissB_13626

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The threat of plastic waste in the environment has evoked rising concern over the past decades. While these versatile and incredibly popular polymer materials undoubtedly fulfil unprecedented services, their extreme durability and alleged toxicity represent major downsides, once in the environment. As plastics break down into smaller microplastics (MP) they evidently pollute almost every thinkable habitat on the globe today. While an estimated 5–12 million tons of plastic end up in the oceans every year, rivers are important pathways, carrying an annual freight of 0.41–4 million tons downstream. The Rhine River, one of Europe’s main streams and one of the World’s busiest waterways, reportedly holds substantial amounts of MP in its near-surface waters and sediments. However, little is known about potential MP sources, seasonal dynamics and the MP pollution of benthic sediments of this major river. In my dissertation I address three pivotal knowledge gaps about MP in the Rhine River and investigate a new type of method to safely and efficiently separate MP from surrounding environmental sample matrices.
The surface water MP pollution of the Rhine River was earlier characterised by the distinct appearance of vast amounts (~60%) of rigid polystyrene microbeads of unknown origin and former purpose. In a sustained investigation of a defined river stretch in the Lower Rhine downstream Cologne, we managed to narrow down the entry region of these pollutants and close-to-certainly unveil the particle’s former purpose as ion-exchange resin beads used in diverse fluid purification applications.
As more data on MP in rivers emerges, an interesting gap opens: empirical field studies tend to generate temporally restricted snapshot data while modellers, laudably seeking the bigger picture, are confronted with enormous uncertainties in their results. In a bid to reduce this void we embarked on a quadruplicate surface water MP observation in the Rhine catchment during 2016–2017. The investigation included three nival discharge regime tributaries and the Rhine in Switzerland as well as a pluvial Rhine River section towards the German-Dutch border. It became evident that despite a coherent increasing MP concentration gradient downstream, reflecting average discharge and catchment size, overall variability in environmental MP data was large. This hampers clear-cut estimations about concentration fluctuations but at the same time reinforces the theory of high MP seasonal pollution fluxes in the European winter months, when Rhine discharge is highest.
Seeking to contribute to the very scarce knowledge of MP and benthic sediment interaction in large dynamic rivers, we took a diving bell and a dredging vessel to the riverbed at two previously identified surface MP hotspots at the German Middle and Lower Rhine. Due to expected water turbulence and flow velocity, substantial settling of MP in such stretches is not necessarily anticipated. Interestingly, it showed that even the Rhine riverbed is not spared from vast MP pollution. The applied research technology allowed for reliable detection of MP down to particle sizes of 11 μm and yielded strongly varying concentrations of 260–11,000 MP kg^–1, with a strongly skewed size class distribution towards the smallest MP particles.
Experience showed us that environmental sample preparation for MP research can be a tedious and resource-intensive enterprise – including health and environmental hazards. Instead of attacking the unwanted portions in a sample (e.g. biogenic residue to isolate MP), a more efficient approach is to select the MP specifically. We refined a proposed lipophilicity-based separation technique and broadened its scope by successfully testing it to four different types of environmental matrices. This one-for-all approach may present a promising means for quicker, cheap, safe and efficient MP data compilation. The method was successfully applied for the seasonal surface MP investigation presented in this dissertation.
Advisors:Holm, Patricia and Segner, Helmut
Faculties and Departments:05 Faculty of Science > Departement Umweltwissenschaften > Integrative Biologie > Aquatische Ökologie (Holm)
UniBasel Contributors:Mani, Thomas and Holm, Patricia and Segner, Helmut
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:13626
Thesis status:Complete
Number of Pages:1 Online-Ressource (249 Seiten)
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Last Modified:06 Aug 2020 04:30
Deposited On:05 Aug 2020 12:43

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